Physical monitoring systems are well known in the art. Conventional monitoring systems typically comprise a reed switch that is electrically connected by wires to an electronic circuit, such as alarm or machinery control system. The reed switch generally comprises a cylindrical glass capsule containing a pair of electrical contacts disposed therein. Each contact is attached to a flexible or movable blade member (i.e., a reed) made of magnetizable material. The reeds are secured to a lead wire that is connected to an electronic circuit. In most applications, at least one of the reeds secured within the capsule is adapted to move toward or away from the other, normally fixed, reed.
A permanent biasing magnet typically actuates the reed switch. The magnet has a magnetic field that is used to magnetize one or both of the reeds, by increasing the magnetic flux in the vicinity of its magnetic portions. Once a reed is magnetized, it will either be attracted to or repel away from the other reed. The magnetization of the reeds is used to open and close the reed switch. When the magnetic flux is reduced, the magnetized reed returns to its normal, unmagnetized condition.
Reed switches are often used in conjunction with external electronic devices, such as security alarms and proximity devices, to name a few. In a typical application, the reed switch is electronically connected to an electronic circuit or loop that is used as a means to set or trigger the security alarm. The reed switch could be either in a normally closed state or a normally open state. In a normally open state, the individual pair of reeds are spaced apart from one another, such that the reed switch is opened. When the reed switch is open, electricity cannot flow through the reeds to the electronic circuit. In a normally closed state, the reeds are in close enough proximity to each other such that the reed switch is closed. When the reed switch is closed, electric current flows through the reeds to the electric circuit. Electrical conductors associated with the electronic circuit lead to a security alarm control unit that is used to set the alarm. The alarm is capable of being set depending on the condition of reed switch being opened or closed.
Proximity devices having reed switches controlled by permanent biasing magnets are typically mounted into movable closure structures. The reed switch is usually mounted in or about a fixed member, such as a frame surrounding a doorway, window, or access panel of a floor. The reed switch has conductors leading out from it to the security or monitoring control unit, such as an alarm control panel. The magnet is mounted into the movable member, such as a door or window that moves relative to the fixed member. The magnetic field of the magnet is used to operate the reeds by magnetizing one or both reeds to open or close the reed switch, thereby controlling the flow of electricity to the alarm. The reeds will remain magnetized or magnetically biased relative to the polarity of the magnetic field of the biasing magnet under which they are influenced. So long as the magnetic field is not moved to a distance in which the reeds are released and return to their normal unbiased or unmagnetized state, the electrical condition of the reed switch will not change. The distance in which the magnet is moved such that the magnetic field releases the reeds and causes the reeds to return to their normal unbiased state, defines the “gap” and “break distance” of the particular proximity device of which the reed switch and magnet are a part.
The gap and break distance for a particular proximity device has been established by industry standards based on acceptable mounting specifications, safety considerations, and market place acceptable. Acceptable gap distances range between 12.5 millimeters (½ inches) for standard gap mounts and 25.5 millimeters (1 inch) for wide gap mounts. However this is fine for protective openings that return to their exact closed position every time. Not all openings do this. Sliding glass doors and windows may have as much as a ½ to ¾ of an inch of movement in the locked closed position. This puts the industries standard right on the edge of operation.
In view of the relatively small tolerances presently used and accepted in the industry for gap and break distances, a problem exists in the use of prior art proximity devices in control devices and physical monitoring systems, such a security alarms. Proximity devices require careful alignment between the reed switch and the biasing magnet which are typically aligned parallel relative to one another along a common axis. In view of the relatively small gap and break distances between the reed switch and the biasing magnet, slight movement of the biasing magnet relative to the reed switch could allow the reeds to be released, resulting in an unnecessary “false alarm”. An example of this problem is found in the use of proximity switches in an overhead door for a garage, as one example.
Overhead doors by design move from a closed position near a floor or a driveway to an open position to allow access to the garage. In both residential and industrial applications, lateral movement or play is designed into the overhead doors to allow the door to move left or right as it rides along its associated, opposed door tracks or guide rails. Manufacturers design play into the door to accommodate the realities of opening and closing a garage door. For instance, door manufacturers anticipate that as a door is opened and closed over time, the alignment of the door will change from its position when first installed simply put, the door will not return to its initial position relative to the floor when the door was first installed. This change in alignment particularly occurs in large industrial doors that are often motorized using an electric motor or lifting mechanism. The torque of the motors that are used to pull the garage door open, will cause the curtain segments of the door to shift laterally as it is being opened or, in some cases, being closed. In anticipation of this occurrence, door manufacturers design the doors or the curtain segments to move laterally as they are being opened or closed so that the door will not jam and thus overtax the electric motor or lifting mechanism.
The play that manufacturers design into garage doors is to keep the doors from binding in the tracks or rails when opening or closing the doors. The wider the door the bigger the lateral play. This can create a problem with proximity devices that require careful alignment for operational stability. After many operations of the door, the lateral shift will place the biasing magnet off from its initial, first installed alignment position that is normally parallel to the reed switch. Once the door shifts out of alignment, it is difficult, if not impossible to use the proximity device to set an alarm until the alignment is returned to at least the position when the proximity device was installed. Therefore, to set the alarm, the door will have to be physically realigned or shifted so that the biasing magnet will be in a position to bias the reeds to operate the reed switch. For example, some commercial doors are 25 feet long and may have as much as 2 inches of lateral play. Therefore, a customer will have to shift the door 1½ inches or so, in order to set the alarm. Most customers, however, will call the security alarm service to advise of a problem with setting the alarm. The security alarm service usually instructs the customer to look at the door to make sure that the biasing magnet is aligned parallel to the reed switch that is typically mounted to the floor. However, to the untrained eye of many customers, it is difficult to identify the problem. To them the door is closed and secure, so something is wrong with the security alarm that was installed. As a result, the customer requires the security alarm service to fix the problem at its own costs. In reality, the security alarm service tries to pass the cost of security alarm servicing to the consumer in the form of a billable service call. It is not the service company's fault that the building has settled or the frame is out of alignment, which has changed the door's closed position. The service company feels justified in passing this labor cost on to the consumer.
Even if the door is initially aligned when the alarm is set, problems with the security alarm still might occur. It is possible for the garage door to move out of alignment after the door is locked and the alarm has been set. Due to the overhead door being out of square, or possibly because a forklift has accidentally adjusted the door during the day, adverse pressure may create binding pressure that may cause the door to move after the door has been closed and secured. The sudden and unanticipated movement of the door causes the biasing magnet to move out of alignment relative to the reed switch, thereby creating a condition in which the alarm may trigger. In the security alarm industry, this is called “swinging” and can result in a false alarm. The shift can be little as ½ inch and thereby cause the reed switch to remain in the open state, creating what is known in the industry as a “can't set” condition. Although the shift in a large overhead door is very gradual, the same problem of swinging can still occur. For instance, it takes a long time for opening and closing pressure to shift the door segments of a commercial door. If a 15 foot tall door has curtain segments that have moved ½ an inch in three years, it moves that much closer to the swinging phenomena. If the door is 25 feet wide it may have as much as 2 inches of factory curtain play built into the design. It would be safe to say that particular type of door after 5 years or hundreds of operations, will move out of alignment such that the bottom rail that typically houses the biasing magnet does not land on the floor exactly at the same place it did the day that the security alarm was installed.
Also influencing the sensitivity of proximity devices and in particular, reed switches, is temperature. Temperature affects the metal reeds as well as the biasing magnets. Changes in temperature will make the material used for the reeds and the biasing magnet to contract and expand. An alarm system may set at the end of the day when temperatures are warmer and appear that all is normal. But a drop in temperature can make the reeds contract. For instance, in the example of the overhead door in which the security alarm is installed, the repeated movement or operation of the door can cause the door to move out of alignment relative to its initial position immediately after it was installed. As a result of the door moving out of alignment, the effective magnitude of the magnetic field that is generated by the biasing magnet which is used to bias the reed switch, is reduced. Thus, as explained previously, the gap or acceptable distance in which the door can move (e.g. laterally) without triggering the security alarm is reduced. As such, a drop in temperature might cause both the magnet and reed switches metals to contract sufficiently to result in a false alarm activation.
Accordingly, the contraction or expansion of the metallic material used to make the reeds or the biasing magnet can impact the location in which the reeds will be biased by the magnetic field of the biasing magnet. Therefore, a change in temperature can cause a change in the location of each reed located within the capsule. The change in temperature may make it difficult for the magnetic field of the biasing magnet to bias one or both reeds sufficiently to operate the reed switch and in turn the security alarm. The end result is that a change in the temperature can change the magnitude and direction of the magnetic field of the magnet as well as the ability of the reeds to open and close the reed switch. For proximity devices and reed switches that operate with a relatively narrow gap, a slight change in the magnet may cause the reed switch to be aligned such that neither pole will have control of the reed switch. As a result, the alarm will not be able to be set or will trigger a false alarm activation.
Another weather related problem is the wind. Wind gusts might cause a garage door or window to move out of alignment after the alarm has been set.
The door or window may move such that the magnetic field of the biasing magnet moves beyond the gap or break distance that is used for the particular proximity device. Again, this slight movement can result in a false alarm.
Adding to the problem of the sensitivity to proximity devices and reed switches, of the prior art, are the structure of the doors or windows themselves. New style vinyl windows and doors have large plastic frames. A window may appear closed to the eye when actually there may be a much as ½ to ¾ of an inch to fully close the opening. If the alarm switch is on the edge but sets at the time of arming the biasing magnet could release the switch later resulting in a false alarm activation.
Many door contacts and sliding windows have a weather seal. The last ½ to ¾ inch of closing requires more pressure to secure the point of contact, namely the seating of the door or window in the frame. Some individuals will attempt to close the opening, but will stop at the weather seal do to the responsive/opposing pressure they feel when hitting the weather seals. Thus, an individual might believe that the opening is closed when it is not. This last ½ to ¾ of an inch sits on the edge of the current arts gap tolerance. If the alarm sets with the opening in this position a false alarm activation could occur.
Accordingly, the precise alignment that is required to set and use a proximity device is a problem in the physical monitoring industry. Physical monitoring security systems that are commercially available in the alarm industry presently allow as little as ½ to 1 inch of play or movement before the switch cannot be set. However, not all magnets or proximity switches are mounted perfectly to all surfaces. This is a common occurrence in the security industry, where the volume of installation of security systems can take precedence over the precise alignment. It is known in the industry that a large number of subcontractors who install physical monitoring systems do so for the short term and are motivated to install the systems quickly and without sufficient care. These contractors are paid on a by the point basis. They receive a set amount of money on each protection point that is installed. So the faster they get the points installed the more money they make per hour. This can lead to some hurried installations with some alarm contacts not being precisely aligned. As a result, the biasing magnet might be just barely aligned relative the reed switch, so that the physical monitoring system will work. This puts the reed switch on the edge of being controlled by the magnetic field. However, the magnetic field will shift out of alignment and require possible resetting by repeated service calls, which is a cost that is often paid for by the consumer.
Although perfect alignment is not an absolute requirement, if the biasing magnet is out of alignment by ½ to ¾ of an inch of its preferred position, problems with setting the alarm and weather will have an increased impact on the ability to set the alarm. For example, the reduction in the temperature at night will cause the metal or other materials used as part of the door and switch to contract as noted previously. The contractions might cause the alignment of the reed switch relative to the biasing magnet to move even further. Therefore, even if the reed switch is aligned sufficient to set the alarm, that condition may change at night when the temperature drops. As the temperature drops, a false alarm might occur because the reed switch has moved out of alignment with the biasing magnet.
Because of the sensitivity of reed switches to slight or momentary movements and changes in temperatures, the reliability of proximity devices have been drawn into question. Today's alarm panels have very sensitive circuitry. Their reaction times are very quick, usually within tenths of a second. All a circuit has to sense is a slight movement in the contacts of a reed switch to generate an alarm. False alarms produced by slight movement of the reed switch relative to the biasing magnet leads to unnecessary multiple police responses and as well as fines incurred by the customer. The company responsible for the installation of the alarm in order to maintain the customer relations in good standing usually pays these fines upon realizing that their installation is at fault. In addition to the fines, the number of times a false alarm is triggered causes police and other law enforcement personnel to direct their attention away from other tasks as well as putting themselves and the public at risk during the response.
Furthermore, each time a false alarm occurs, a technician might be required to realign the relative position between the reed switch and the biasing magnet. This becomes costly and reduces the ability to discern whether an alarm is triggered because of an intruder or because of some other reason. Many cities have adopted special ordinances to combat false alarm problems. In addition, in a number of communities, residents have formed committees to combat the problem of false alarms in their neighborhood and the resulting injuries and hazards that are suffered by police and others in responding to false alarms. Indeed, municipalities have imposed significant fines to ensure a resolution is addressed to a repetitive false alarm problem. Some responding agencies have adopted a no response policy unless verified. This requires a second or third party to respond first and identify that a real crime is occurring, before the local police agency will respond.
Prior art solutions to the problem with proximity devices have been unsuccessful in resolving lateral shifting problems associated with magnetic reed switches. The industry has been known to use larger magnets. These are combined with reed switches and are referred to as wide gap contacts. They do offer a larger gap distance to control the distance but only in the vertical lift distance. The problem with lateral slide play cannot be addressed by the wide gap switches. The problem resides in the physics of the poles of the magnet. As the magnet moves, one pole looses control of the reed. The other pole starts to cross the center of the reed, when the pole is near the center of the parallel reed it cannot maintain control of the reed. The closer to the center the less field strength the magnet has to hold the reed's stability. This, combined with the fast speed of the alarm circuit, is where unnecessary false alarms are generated. There are many different types of openings that require proximity protection that have factory designed lateral play built into the normal operation. Many of these openings play exceed the industry gap control distance. Airplane hangers, barn doors, large commercial steel sectional curtain overhead doors and double sliding glass doors to name a few.
Other attempts to solve the problems associated with reed switches and proximity devices have been by manipulating the location and use of the biasing magnets. For instance, Holce, U.S. Pat. No. 4,213,110 shows a proximity switch having adjustable sensitivity. The sensitivity of the reed switch is adjusted by varying the position of the biasing magnet. Varying the position of the biasing magnet adjusts the distances between the switch and the biasing magnet at which the switch will actuate and release for a given actuating magnet. Holce teaches that by adjusting the distance of the biasing magnet, smaller magnets for a given separation makes the device less expensive to produce, more easily concealed from sight, and more difficult to detect. However, Holce does not teach how to better control the sensitivity of the proximity devices through the use of an improved magnetic assembly that is relatively low in cost. Also, Holce does not teach the use of an enhanced magnetic assembly that provides the flexibility to design the amount of gap or location of the break distance that is desired, beyond present industry standards.
Therefore, it is desired to provide a magnetic apparatus to increase and control the gap or break distance used for proximity devices, particularly those used in physical security monitoring or position control systems. In particular, it is desired to provide an enhanced magnetic assembly, comprising the use of multiple, aligned alike magnets to control external electronic devices, such as a physical security monitoring system. Still yet, it is further desired to provide a magnetically operated system that is adjustable, creates a wider gap, and is inexpensively manufactured. It is also desired to provide a magnetic assembly to create a wider gap to permit the venting of a room, yet maintain the electrical condition of the physical security monitoring system. These and other features of the present invention are described in further detail below.